Environmental influences on Acinetobacter sp. strain BD413 transformation in soil

Abstract

The ability of various environmental factors (root exudate from silver tussock, blue tussock, flax, wheat, ryegrass and lupin; simulated-root exudate; moisture; temperature; soil density; salinity; sewage sludge; fertiliser; pesticide) to promote or inhibit transformation of the soil-dwelling bacterium Acinetobacter baylyi BD413 (pFG4ΔnptII) was investigated using soil microcosm studies. A marker-rescue system was used to monitor the transfer of a functional nptII gene from exogenous chromosomal DNA to A. baylyi BD413 (pFG4ΔnptII). Significant differences were detected in A. baylyi BD413 (pFG4ΔnptII) transformation rates in three sterile New Zealand agricultural soils. Addition of simulated-root exudate to the sterile soil was essential for transformation of A. baylyi BD413 (pFG4ΔnptII) in the soil types tested, but addition of plant exudates collected from a variety of New Zealand cropping and native plants did not promote transformation rates to above detectable limits. Increases in soil temperature and bulk density increased the transformation rate but this effect was not consistent across all three soil types. Application of sewage sludge to sterile soils significantly increased transformation in the sandy soil but not in the silt loam and fine sandy loam soil types. Fertiliser (superphosphate) and herbicide (glyphosate) applied at agronomic rates did not affect transformation rates; however, when used at 5× and 50× the agronomic rate respectively, transformation was significantly reduced in all three sterile soils. These results suggest that competence and transformation of the A. baylyi BD413 (pFG4ΔnptII) in soils is highly dependent on the presence of nutrients and is also influenced by the soil texture.